CVE-2021-21249Public exploitNetwork attack vector

Authenticated code execution via unsafe YAML class instantiation

Published Jan 15, 2021 · Updated Aug 3, 2024

Unsafe YAML deserialization in OneDev before 4.0.3 allows remote authenticated users to execute arbitrary code through a crafted BuildSpec. VersionedYamlDoc's SnakeYAML constructor accepts attacker-selected type tags and instantiates unapproved Java classes, including a URL-loaded script engine provider. Authenticated access able to provide a BuildSpec is required, and successful exploitation executes code in the server process.

CVSS severity9.6
Critical
EPSS probability2.93%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Unsafe YAML deserialization in OneDev before 4.0.3 allows remote authenticated users to execute arbitrary code through a crafted BuildSpec. VersionedYamlDoc's SnakeYAML constructor accepts attacker-selected type tags and instantiates unapproved Java classes, including a URL-loaded script engine provider. Authenticated access able to provide a BuildSpec is required, and successful exploitation executes code in the server process.

The record

CVE
CVE-2021-21249
Published
Jan 15, 2021
Updated
Aug 3, 2024
Vendor
OneDev Pty
Product
OneDev
Classifications
CWE-502, CWE-74, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 4.0.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

OneDev Pty · OneDevversion=< 4.0.3

Published CVSS scores

6.5NIST NVDAV:N/AC:L/Au:S/C:P/I:P/A:P
9.6GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N
8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
CWE-74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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